Various printing methods, which have hitherto been extensively used for full-color image formation, include: a sublimation dye thermal transfer method wherein a dye contained in a colorant layer is transferred by thermal sublimation and diffusion onto an image-receiving sheet; a thermal ink transfer method wherein a colorant layer is melt and softened upon heating and as such is transferred onto an image-receiving sheet; an ink jet recording method; and electrophotography.
They are utilized, for example, in many booklets such as passports, identification cards, driving licenses, commuter's tickets, and membership cards, and in the preparation of cards and photographs for business, or in printers of personal computers or video printers.
In the case of prints formed by thermal dye transfer (sublimation dye thermal transfer) and ink jet recording, however, when they are brought into contact with solvents, chemicals and the like such as water and alcohols which are near at hand, or when they are stored in contact with plasticizer-containing card cases, file sheets, plastic erasers or the like, images are blurred, or otherwise, dyes are transferred onto these articles resulting in contamination of the card cases, or discoloration by light.
A method known for protecting the above images against solvents, chemicals or the like is to transfer a thermally transferable resin layer using a protective layer transfer sheet comprising a thermally transferable resin layer with a thermal head, a heating roll or the like to form a protective layer.
Regarding this protective layer transfer sheet, for example, Japanese Patent Laid-Open No. 240404/2002 discloses a technique for providing a protective layer transfer sheet characterized by comprising a substrate sheet and a thermally transferable protective layer provided on at least a part of one side of the substrate sheet, the protective layer being a laminate having a structure of at least two layers of a layer composed mainly of at least an acrylic resin and a layer composed mainly of a polyester resin provided in that order on the substrate sheet.
However, for example, in a field of ID cards in which letter information and an image of a facial photograph should remain unchanged or should not be deteriorated for a long period of time, durability such as folding resistance and scratch resistance, plasticizer resistance, transparency, layer transferability and the like which are further superior to those in the protective layer transfer sheet described in the above publication are desired.